Effect of vehicle weight on natural frequencies of bridges measured from traffic-induced vibration

Recently,ambient vibration test(AVT)is widely used tu estimate dynamic characteristics of large civil struc- tures.Dynamic characteristics ean be affected by various envirnnmental factors such as humidity,intensity of wind,and temperature.Besides these environmental conditions,tire mass of vehicles may change the measured valnes when traffic-in- duced vibration is used as a source of AVT tor bridges.The effect of vehicle mass on dynamic characteristics is investigated through traffic-induced vibration tests on three bridges;(1)three-span suspension bridge(128m+404m+128m),(2) five-span continuous steel box girder bridge(59m+3@ 95m+59m),(3)simply supported plate girder bridge(46m). Acceleration histories of each measurement location under normal traffic are recorded for 30 minutes at field.These recor- ded histories are divided into individual vibrations and are combined into two groups aceording to the level of vibration;one by heavy vehicles such as trucks and buses and the other by light vehicles such as passenger cars.Separate processing of the two groups of signals shows that,for the middle and long-span bridges,the difference can be hardly detected,but,for the short span bridges whose mass is relatively small,the measured natural frequencies can change up to 5.4%.

Pd catalysts supported on modified Zr_(0.5)Al_(0.5)O_(1.75) used for lean-burn natural gas vehicles exhaust purification

Composite supports Zr0.5Al0.5O1.75 modified by metal oxides, such as La2O3, ZnO, Y2O3 or BaO, were prepared by co-precipitation method, and palladium catalysts supported on the modified composite supports were prepared by impregnation method. Their properties were characterized by X-ray diffraction （XRD）, NH3 temperature-programmed desorption （NH3-TPD）, He temperature-programmed reduction （He-TPR）, N2 adsorption/desorption, and CO-chemisorption. The catalytic activity and the resistance to water poisoning of the prepared Pd catalysts were tested in a simulated exhaust gas from lean-burn natural gas vehicles with and without water vapor. The results demonstrated that the modified supports had an apparent effect on the performance of Pd catalysts, compared with the Pd catalyst supported on the unmodified ZrA1. The addition of ZnO or Y203 promoted the conversion of CH4. In the absence of water vapor, Pd/ZnZrA1 exhibited the best activity for CH4 conversion with the light-off temperature （Tso） of 275 ℃ and the complete conversion temperature （T90） of 314 ℃, respectively. However, in the presence of water vapor, Pd/YZrA1 was the best one over which the light-off temperature （Tso） of methane was 339 ℃ and the complete conversion temperature （T90） was 371 ℃. These results indicated that Pd catalyst supported on the modified composite ZrA1 support showed excellent catalytic activity at low temperature and high resistance to H20 poisoning for the exhaust purification of lean-burn natural gas vehicles.

Excellent complete conversion activity for methane and CO of Pd/TiO_2-Zr_(0.5)Al_(0.5)O_(1.75) catalyst used in lean-burn natural gas vehicles

Palladium catalysts are supported on TiO2, ZrO2, A12O3, Zro.sAlo.501.75 and TiO2-Zro.sAlo.501.75 prepared by co-precipitation method, re- spectively. Catalytic activities for methane and CO oxidation are evaluated in a gas mixture that simulated the exhaust from lean-burn natural gas vehicles （NGVs）. Pd/TiO2-Zro.sAlo.501.75 performs the best catalytic activity among the tested five catalysts. For CH4, the light-off temperature （Tso） is 254 ℃, and the complete conversion temperature （Tgo） is 280 ℃; for CO, Tso is 84 ℃, and Tgo was 96 ℃. Various techniques, including N2 adsorption-desorption, X-ray diffraction （XRD）, H2-temperature-programmed reduction （H2-TPR）, X-ray photoelec- tron spectroscopy （XPS）, and scanning electron microscopy （SEM） are employed to characterize the effect of supports on the physicochemical properties of prepared catalysts. N2 adsorption-desorption and SEM show that TiO2-Zro.5Al0.501.75 expresses uniform nano-particles and large meso-pore diameters of 26 nm. H2-TPR and XRD indicate that PdO is well dispersed on the supports and strongly interacted with each other. The results of XPS show that the electron density around PdO and the proportion of active oxygen on TiO2-Zro.sAl0.501.75 are maxima among the five supports.

Petroleum substitution, greenhouse gas emissions reduction and environmental benefits from the development of natural gas vehicles in China

This study develops a bottom-up model to quantitatively assess the comprehensive effects of replacing traditional petroleum-powered vehicles with natural gas vehicles（NGVs） in China based on an investigation of the direct energy consumption and critical air pollutant（CAP） emission intensity, life-cycle energy use and greenhouse gas（GHG） emission intensity of NGV fleets. The results indicate that, on average, there are no net energy savings from replacing a traditional fuel vehicle with an NGV. Interestingly, an NGV results in significant reductions in direct CAP and life-cycle GHG emissions compared to those of a traditional fuel vehicle, ranging from 61% to 76% and 12% to 29%, respectively. Due to the increasing use of natural gas as a vehicle fuel in China（i.e. approximately 28.2 billion cubic metres of natural gas in2015）, the total petroleum substituted with natural gas was approximately 23.8 million tonnes（Mt）, which generated a GHG emission reduction of 16.9 Mt of CO2 equivalent and a CAP emission reduction of 1.8 Mt in 2015. Given the significant contribution of NGVs, growing the NGV population in 2020 will further increase the petroleum substitution benefits and CAP and GHG emission reduction benefits by approximately 42.5 Mt of petroleum-based fuel, 3.1 Mt of CAPs and 28.0 Mt of GHGs. By 2030, these benefits will reach 81.5 Mt of traditional petroleum fuel, 5.6 Mt of CAPs and 50.5 Mt of GHGs, respectively.

CeO_2-ZrO_2-La_2O_3-Al_2O_3 composite oxide and its supported palladium catalyst for the treatment of exhaust of natural gas engined vehicles

Composite supports CeO2-ZrO2-Al2O3（CZA） and CeO2-ZrO2-Al2O3-La2O3（CZALa） were prepared by co-precipitation method. Palladium catalysts were prepared by impregnation and their purification ability for CH4, CO and NOx in the mixture gas simulated the exhaust from natural gas vehicles （NGVs） operated under stoichiometric condition was investigated. The effect of La2O3 on the physicochemical properties of supports and catalysts was characterized by various techniques. The characterizations with X-ray diffraction （XRD） and Raman spectroscopy revealed that the doping of La2O3 restrained effectively the sintering of crystallite particles, maintained the crystallite particles in nanoscale and stabilized the crystal phase after calcination at 1000 ℃. The results of N2-adsorption, H2-temperatnre-programmed reduction （H2-TPR） and oxygen storage capacity （OSC） measurements indicated that La2O3 improved the textural properties, reducibility and OSC of composite supports. Activity testing results showed that the catalysts exhibit excellent activities for the simultaneous removal of methane, CO and NOx in the simulated exhaust gas. The catalysts supported on CZALa showed remarkable thermal stability and catalytic activity for the three pollutants, especially for NOx. The prepared palladium catalysts have high ability to remove NOx, CH4 and CO, and they can be used as excellent catalysts for the purification of exhaust from NGVs operated under stoichiometric condition. The catalysts reported in this work also have significant potential in industrial application because of their high performance and low cost.

Effect of cobalt oxide on performance of Pd catalysts for lean-burn natural gas vehicles in the presence and absence of water vapor

Pd-based catalysts modified by cobalt were prepared by co-impregnation and sequential impregnation methods,and characterized by X-ray powder diffraction （XRD）,N2 adsorption/desorption （Brunauer-Emmet-Teller method）,CO-chemisorption and X-ray photoelectron spectroscopy （XPS）.The activity of Pd catalysts was tested in the simulated exhaust gas from lean-burn natural gas vehicles.The effect of Co on the performance of water poisoning resistance for Pd catalysts was estimated in the simulated exhaust gas with and without the presence of water vapor.It was found that the effect of Co significantly depended on the preparation process.PdCo/La-Al2O3 catalyst prepared by co-impregnation exhibited better water-resistant performance.The results of XPS indicated that both CoAl2O4 and Co3O4 were present in the Pd catalysts modified by Co.For the catalyst prepared by sequential impregnation method,the ratio of CoAl2O4/Co3O4 was higher than that of the catalyst prepared by co-impregnation method.It could be concluded that Co3O4 played an important role in improving water-resistant performance.

Development of Natural Gas Vehicle(NGV) Industry in China

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Non-pneumatic mechanical elastic wheel natural dynamic characteristics and influencing factors

Non-pneumatic tire appears to have advantages over traditional pneumatic tire in terms of flat proof and maintenance free.A mechanical elastic wheel(MEW) with a non-pneumatic elastic outer ring which functions as air of pneumatic tire was presented.The structure of MEW was non-inflatable integrated configuration and the effect of hinges was accounted for only in tension. To establish finite element model of MEW, various nonlinear factors, such as geometrical nonlinearity, material nonlinearity and contact nonlinearity, were considered. Load characteristic test was conducted by tyre dynamic test-bed to obtain force-deflection curve. And the finite element model was validated through load characteristic test. Natural dynamic characteristics of the MEW and its influencing factors were investigated based on the finite element model. Simulation results show that the finite element model closely matched experimental wheel. The results also show that natural frequency is related to ground constraints, material properties, loads and torques. Influencing factors as above obviously affect the amplitude of mode of vibration, but have little effect on mode of vibration shape. The results can provide guidance for experiment research, structural optimization of MEW.

Current State and Prospect of China Natural Gas Industry

Natural gas output remained stable growth and reached 130.9 billion cubic meters in 2015, 3% higher than the same period last year. Shale gas saw huge progress. China thus became the third country in the world fulfilling commercial development after U.S. and Canada. Natural gas import growth and growth rate declined obviously, and the imported pipeline gas and LNG totaled 61.2 billion cubic meters in 2015. Apparent natural gas consumption was 186.5 billion cubic meters in 2015, rising by 4.4% as compared with the same period last year, but it hit a historic low. There is higher downward pressure on domestic macro economy in 2016. However, natural gas demand will see more rapid growth, propelled by such favorable factors as gas price regulation and environmental protection policies. It is prospected that natural gas market will take a turn for the better than in 2015, and natural gas supply will still be rich in general in 2016.

Development Status and Prospects of the Natural Gas Industry in China

The year 2017 saw explosive growth in China's natural gas market, and the apparent consumption was 235.7 billion cubic meters, up 18.2% over the same period of 2016. In 2017, China's domestic production growth picked up significantly, reaching 145.3 billion cubic meters, an increase of 9%.Natural gas imports grew rapidly, and imported pipeline gas and imported LNG totaled 91.6 billion cubic meters. The trade volume of LNG surpassed that of pipeline gas for the first time since 2012. In 2018, the macro-economy is expected to maintain growth at a moderate-to-high rate. However, driven by favorable factors such as environmental policies, China's demand for natural gas is expected to continue to grow rapidly, and natural gas consumption will maintain double-digit growth, roughly at 12%. Nevertheless, the seasonable imbalance between natural gas supply and demand will remain conspicuous.

临近车辆对LNG槽车泄漏扩散规律的影响研究

为降低LNG槽车行驶过程中发生泄漏对临近车辆造成爆炸威胁的可能性,通过CFD数值模拟,研究LNG泄漏在临近车辆周围的浓度分布特征,研究车辆间距等因素对LNG泄漏扩散过程的影响规律。研究表明:在风速2m/s,泄漏孔径0.1m,LNG泄漏口下风向10、20、30m处,空间内甲烷气云的流动状态和浓度分布趋势基本保持不变,泄漏口轴心处甲烷气体流速最高并向周围依次递减;临近车辆的阻挡作用使得高浓度甲烷气云积聚于车头处,随着临近车辆间距的增加,其后方出现回流,流场分布形态更加紊乱,易出现甲烷气云积聚现象;LNG槽车与临近车辆间距为30m且泄漏10s内,临近车辆周围的甲烷气云浓度低于爆炸下限,建议后方车辆宜与LNG槽车保持30m以上的安全距离。

水凝胶延迟水下回转体边界层自然转捩机理研究

水下航行体首部声纳探测能力与边界层转捩密切相关。本文开展了水凝胶超材料在延迟水下航行体边界层自然转捩方面的应用基础研究,并探究了其内在机理。在高速水洞中分别开展了刚性和水凝胶表面的SUBOFF模型总阻力系数与二维瞬时速度场大视场PIV实验测试,采用多路径积分算法对SUBOFF模型周围脉动压力场进行估算;结合刚性SUBOFF模型边界层流动线性稳定性分析与PIV流场测试结果,获得刚性SUBOFF模型边界层自然转捩特性;采用“比光强”算法,对低速水洞中水凝胶表面SUBOFF模型局部形变与近壁区速度场进行频谱分析,揭示水凝胶表面流−固耦合作用机制;基于法向瞬时速度分量的连续子波变换,对边界层瞬时流场间歇性进行分析,揭示水凝胶在流−固耦合作用下延迟SUBOFF模型边界层自然转捩的机理。

混合动力汽车功率分流传动系统扭转振动及其影响因素研究

针对某款混合动力汽车,综合考虑发动机、电机、复合行星齿轮机构、离合器、减速器、差速器和半轴等部件,采用集中质量法建立功率分流传动系统动力学模型。在此基础上,分析不同运行工况下传动系统固有频率和振型,分别研究电机和发动机激振频率与传动系统固有频率之间的关系,仿真分析扭转减振器刚度对传动系统固有频率的影响规律,通过改变扭转减振器刚度从而使得传动系统共振转速远离发动机常用工作区。

基于无人机高光谱的内蒙古天然牧草氮磷钾含量的反演

氮(Nitrogen,N)、磷(Phosphorus,P)、钾(Kalium,K)含量是衡量牧草营养价值的重要指标,其准确检测对于草地退化评价和畜牧业发展具有重要意义。本研究以内蒙古温性荒漠草原和温性草原为研究对象,结合高光谱无人机数据和地面实测数据,使用最小绝对值收缩和选择算子(Lasso)回归来进行敏感波段筛选,然后采用偏最小二乘回归(Partial ieast squares regression,PLSR)和随机森林(Random forest,RF)算法分别构建天然牧草N,P,K含量的估测模型。结果表明:一阶导数(First derivative,FD)和对数的倒数(Reciprocal of logarithm,Log(1/R))处理有助于提高敏感波段与N,P,K含量的相关性;Lasso回归方法可以大大地减少波段的数量;两种草地类型下N和K含量构建的最佳反演模型均为RF模型,R^(2)在0.76~0.90之间;P含量在温性荒漠草原下最优的是PLSR模型,R^(2)为0.72,而在温性草原下为RF模型(R^(2)=0.75)。研究结果对于草地分等定级、放牧管理和草地农业等都具有重要参考价值。

Potential effects of automated driving on vehicle travel demand: A comparison of three case cities

Automated vehicles(AVs)hold the potential to reduce road accidents,mitigate traffic congestion,and improve travel experience.However,the possible countervailing impacts from the changes in underserved populations’vehicle travel demand tend to be overlooked.To determine the vehicle travel demand changes that resulted from underserved populations aged between 6 and 80,this paper explores the latent effect of AVs on vehicle kilometers traveled(VKT)in a fully AV environment using person trip survey data from the cities of Sanya,Shijiazhuang,and Shenzhen in China.This paper uses the natural decline hypothesis of travel demand and proposes a regression model to investigate the difference among the cities’latent vehicle travel demand.Results show that the average VKT of the overall population in Sanya,Shijiazhuang,and Shenzhen increased by 33.4%,47.0%,and46.8%,respectively.The analysis of the regression model confirms that the current travel behavior of individuals can affect the degree of increase in their average VKT.Integrating AVs into public transport,increasing the acceptance of automated shared mobility options,transforming road space use type,and prototyping AV designs with various features and needs are potential methods to cope with the countervailing impacts.The total VKT of the overall population increased by approximately 10%-25%depending on the city.The conclusions of this paper provide informative insights into the evaluation of VKT for underserved populations and contribute to the deployment of AVs to address equity and inclusion issues.

基于激光遥感的甲烷泄漏源搜索系统

为了弥补传统人工在天然气生产、运输和存储过程甲烷泄漏巡检中存在的劳动强度大、容易漏检、耗时耗力等不足,提出了一种基于激光遥感吸收光谱技术的甲烷泄漏搜索系统.选用近红外1653.7 nm的TO封装DFB激光器作为光源,以收发一体的卡塞格林光学结构进行发射激光和接收来自反射回来的微弱光信号,采用嵌入式单片机实现光信号的调制与解调.以开源ArduPilot AMP2.8作为无人机的飞控,采用433 MHz无线模块进行甲烷泄漏数据实时传送,计算机接收端以LabView虚拟仪器开发了接收应用程序进行数据的接收、显示和存储.以体积分数为10-3的甲烷气袋为搜索目标,采用Z字形搜索算法模拟了现场甲烷泄漏搜索实验.实验结果表明,该算法具有较高的检测精度和定位准确性,能够准确地检测到甲烷泄漏源位置.这为天然气泄漏源的快速检测和定位提供了有效的技术支持.

压缩天然气汽车压力标准现状分析及发展建议

文章主要论述了我国压缩天然气汽车压力标准现状,通过归纳压缩天然气汽车压力标准体系及分析提高压缩天然气汽车压力标准意义,探讨提高压力标准实施的目标及条件,最后提出切实可行的建议,以期为相关人员提供参考。

“双积分”政策与新能源汽车企业经营绩效:一项准自然实验

本文基于2013—2020年中国27家新能源汽车上市企业的面板数据,采用PSM-DID的方法考察“双积分”政策实施对新能源汽车企业经营绩效的影响。研究发现:(1)“双积分”政策显著提高了新能源汽车上市公司的经营绩效,即新能源汽车企业可以将双积分政策带来的规制压力内化为企业经营的动力,该结论在一系列稳健性检验中依然成立;(2)在作用机制方面,“双积分”政策通过提高企业的研发投入与汽车销量将规制压力内化为企业经营的动力,从而最终提升其经营绩效;(3)异质性分析表明,当产权性质为国有、企业规模较大以及政策施行时间较长时,“双积分”政策对企业经营绩效的促进效果更显著。

广西应急测绘保障体系框架研究

分析了广西应急测绘任务需要解决的问题,包括:应对的情况、保障服务的对象、保障的阶段和各阶段的主要工作等。提出了该问题的解决思路,设定了广西应急测绘保障体系建设目标,设计了一套具有“统一指挥、上下联动、依靠群众”组织体系的,具有“专常兼备、反应迅速”技术体系的和“覆盖全面”支撑体系的广西应急测绘保障体系框架,很好支撑了首次国省协同跨省区应急测绘保障演练的顺利开展,也经受住了“‘3.21’东航飞行事故”应急测绘保障任务的实践考验。

天燃气重型商用车制造工艺技术流程研究

为研究天然气商用车与传统商用车(柴油)的能源性质差异,阐述了燃料特性、加注设备成本、常见泄漏情形和商用车污染物及温室气体的排放情况、续航能力等内容,对天然气商用车供气系统气瓶及气路结构、原理进行分析说明,并对国内某重型商用车供气系统布置形式进行分解,制定了天然气重型商用车的装配工艺流程及工艺规范。最后,研究了GB 19239—2022《燃气汽车燃气系统安装规范》的泄漏试验操作规程,参考氮气置换技术,梳理了天然气重型商用车的氮气置换操作规程和天然气重型商用车从装配到入库的生产工艺。